sync.WaitGroup不等待

huangapple
go评论108阅读模式
英文:

sync.WaitGroup doesnt waits

问题

也许我没有看到明显的问题，我做错了什么：

  1. func printSize(listOfUrls []string) {
  2.     var wg sync.WaitGroup
  3.     wg.Add(len(listOfUrls))
  4.     for _, myurl := range listOfUrls {
  5.         go func() {
  6.             body := getUrlBody(myurl)
  7.             fmt.Println(len(body))
  8.             wg.Done()
  9.         }()
  10.     }
  11.     wg.Wait()
  12. }

如果我移除 wg 和 go，我可以正确地接收到每个 URL 正文的大小。但是按照上面的方式，它几乎立即打印出零。getUrlBody() 有时需要执行几分钟。

回答评论：我也尝试了这种方式，为了确保，它表现出相同的行为。
我发现错误出现在 getUrlBody 和 main() 函数中...

  1. func printSize(listOfUrls []string) {
  2.     var wg sync.WaitGroup
  3.     wg.Add(len(listOfUrls))
  4.     for _, myurl := range listOfUrls {
  5.         go f(myurl, &wg)
  6.     }
  7.     wg.Wait()
  8. }
  10. func f(myurl string, wg *sync.WaitGroup) {
  11.     body := getUrlBody(myurl)
  12.     fmt.Println(len(body))
  13.     wg.Done()
  14. }
英文:

May be I can not see obvious thing, what am I doing wrong:

  1. func printSize (listOfUrls []string){
  2. 	var wg sync.WaitGroup
  3.     wg.Add(len(listOfUrl))
  4.     for _, myurl := range(listOfUrls){
  5.         go func(){
  6.                body := getUrlBody(myurl)
  7.                fmt.Println(len(body))
  8.                wg.Done()
  9.            }()    
  10.     } 
  11.     wg.Wait()
  12. }

If I remove wg and go, I receive the size of each url body correctly. If I do it as in above, it prints zeroes almost instantly. The getUrlBody() takes time to execute sometimes minutes.

Answering comment: I also tried it this way, to be sure, and it demonstrate same behaviour.
I found the error was in getUrlBody and main() function...

  1. func printSize(listOfUrls []string) {
  2.     var wg sync.WaitGroup
  3.     wg.Add(len(listOfUrls))
  4.    	    for _, myurl := range listOfUrls {
  5. 	      go f(myurl, &wg)
  6.         }
  7.     wg.Wait()
  8. }
  10. func f(myurl string, wg *sync.WaitGroup) {
  11.     body := getUrlBody(myurl)
  12.     fmt.Println(len(body))
  13.     wg.Done()
  14.  }

答案1

得分: 2

所有的goroutine都共享单个myurl变量。请参阅https://golang.org/doc/faq#closures_and_goroutines获取更多信息。

将代码更改为：

  1. func f(listOfUrls []string){
  2.   var wg sync.WaitGroup
  3.   wg.Add(len(listOfUrl))
  4.   for _, myurl := range(listOfUrls){
  5.     go func(myurl string){
  6.            body := getUrlBody(myurl)
  7.            fmt.Println(len(body))
  8.            wg.Done()
  9.        }(myurl)    
  10.   } 
  11.   wg.Wait()
  12. }

或者

  1. func f(listOfUrls []string){
  2.   var wg sync.WaitGroup
  3.   wg.Add(len(listOfUrl))
  4.   for _, myurl := range(listOfUrls){
  5.     myurl := myurl
  6.     go func(){
  7.            body := getUrlBody(myurl)
  8.            fmt.Println(len(body))
  9.            wg.Done()
  10.        }()    
  11.   } 
  12.   wg.Wait()
  13. }
英文:

All of the goroutines are sharing the single myurl variable. See https://golang.org/doc/faq#closures_and_goroutines for more information.

Change the code to:

  1. func f(listOfUrls []string){
  2.   var wg sync.WaitGroup
  3.   wg.Add(len(listOfUrl))
  4.   for _, myurl := range(listOfUrls){
  5.     go func(myurl string){
  6.            body := getUrlBody(myurl)
  7.            fmt.Println(len(body))
  8.            wg.Done()
  9.        }(myurl)    
  10.   } 
  11.   wg.Wait()
  12. }

or

  1. func f(listOfUrls []string){
  2.   var wg sync.WaitGroup
  3.   wg.Add(len(listOfUrl))
  4.   for _, myurl := range(listOfUrls){
  5.     myurl := myurl
  6.     go func(){
  7.            body := getUrlBody(myurl)
  8.            fmt.Println(len(body))
  9.            wg.Done()
  10.        }()    
  11.   } 
  12.   wg.Wait()
  13. }

huangapple
  • 本文由 发表于 2015年6月2日 01:39:05
  • 转载请务必保留本文链接：https://go.coder-hub.com/30579752.html
  • concurrency
  • go
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